Semitransparent Sb₂S₃ thin film solar cells by ultrasonic spray pyrolysis for use in solar windows

The integration of photovoltaic (PV) solar energy in zero-energy buildings requires durable and efficient solar windows composed of lightweight and semitransparent thin film solar cells. Inorganic materials with a high optical absorption coefficient, such as Sb₂S₃ (>10⁵ cm^-1 at 450 nm), offer semitransparency, appreciable efficiency, and long-term durability at low cost. Oxide-free throughout the Sb₂S₃ layer thickness, as confirmed by combined studies of energy dispersive X-ray spectroscopy and synchrotron soft X-ray emission spectroscopy, semitransparent Sb₂S₃ thin films can be rapidly grown in air by the area-scalable ultrasonic spray pyrolysis method. Integrated into a ITO/TiO₂/Sb₂S₃/P3HT/Au solar cell, a power conversion efficiency (PCE) of 5.5% at air mass 1.5 global (AM1.5G) is achieved, which is a record among spray-deposited Sb₂S₃ solar cells. An average visible transparency (AVT) of 26% of the back-contact-less ITO/TiO₂/Sb₂S₃ solar cell stack in the wavelength range of 380-740 nm is attained by tuning the Sb₂S₃ absorber thickness to 100 nm. In scale-up from mm² to cm² areas, the Sb₂S₃ hybrid solar cells show a decrease in efficiency of only 3.2% for an 88 mm² Sb₂S₃ solar cell, which retains 70% relative efficiency after one year of non-encapsulated storage. A cell with a PCE of 3.9% at 1 sun shows a PCE of 7.4% at 0.1 sun, attesting to the applicability of these solar cells for light harvesting under cloud cover.